• It is important to know how to control printing of data. It is recommended that you open a file for print out. The PRINT statement may send information to the terminal screen where it may scroll past. An alternative is to copy the UNIX output file to a name of your choice (and use print commands).

• Assigning a print file named PROB.OUT for formatted data
  In the FORTRAN code, before any writing commands are done, insert the line:

  OPEN(UNIT=7,NAME='PROB.OUT',FORM='FORMATTED',STATUS='UNKNOWN')

  This command assigns the unit number (=7) to which you will write the formatted information. Use a CLOSE command before you end your program; otherwise, the compiler may or may not close the file for you at the end of execution.

  Remember to close the unit before your program terminates; i.e.: CLOSE(7)

• Three commands related to printing
  • The FORMAT command
    • where you specify the way in which you would like the information to be printed
  • The PRINT command
    • sends output to the default output
    • example
                  PRINT 5, t
      5         FORMAT (E12.2)
    • another ex.
                  PRINT *, t
  • The WRITE command
    • sends output to the file you have specified in an OPEN statement
    • example
                  WRITE(7,5) t
      5           FORMAT (E12.2)
    • another ex. (makes 10 columns)
                  WRITE(7,8) (A(J),J=1,10)
      8           FORMAT (10F8.2)

• Some example formats:
  • "A" format: used for text strings. e.g. A10 prints 10 characters.
  • "F" format: used for floating point numbers. e.g. F7.2 allows 4 numbers before the decimal and 2 after the decimal. Note that the decimal "period" is counted as one of the 7 places reserved by F7.2
    If the variable is negative, a space for the minus signe is needed, leaving only 3 numbers before the decimal.
  • "I" format: used for integers. e.g. I5 reserves 5 spaces for an integer number if positive. If negative, 4 spaces.
  • What if your number exceeds the available spaces? Most compilers will display a bunch of asterisks: i.e. ****.** or *****
    Note: A common situation is to neglect to include the space needed to print the minus sign for a negative number.
  • "E" format: used for scientific notation. Note: need to leave space for the "e" (meaning power of 10), the sign of the power, and the size of the power. The amount of space needed varies with the compiler & operating system. e.g. E10.3 often is just enough spaces (10) to have the sign, one place left of the decimal and 3 spaces to the right plus all the power of 10 information.
  • "G" format: the computer chooses a combination of F, E and sometimes I formats based on the data.
    Note: while G sounds like a simple solution, you often use formated writes to create columns of fixed width or other consistent ordering. Since G format may vary which of E or F it uses, you may not get consistent ordering when it is used.

• The 'wild card' character " * " lets the computer choose the format. This is:
  1. most often used with the print command. e.g. PRINT *,t
  2. useful if you want a quick print for debugging purposes
  3. useful if you don't know the magnitude of the item to be printed (and don't wish to use E format)
  4. very simple and thus easy to use -- you don't have a FORMAT statement
  5. undesirable if you want to organize your output neatly. e.g. into tidy columns.

• Carriage control:
  • "T" is "tab" and it does not format data but can be used to space over e.g. T15 goes over 15 spaces.
  • "X" is very similar to tab: 15x goes over 15 spaces
  • "/" is used to indicate carriage return.

• Printing Character strings
  • "H" is used to print text using hollerith format: e.g. 10hPrint this will print the letters "Print this". Notice that space(s) are counted as well. Obviously, counting the number of letters and spaces is quite tedious, so...
  • " 'character string ' " enclosing the characters you want printed within single quotes works like the hollerith command without having to count and specify the number of characters. e.g. 'Print this' will print the letters "Print this".

• Hint: try to avoid setting up printing calls that are very wide, they may print with a confusing word wrap, may be difficult to view in a file editor, might even be truncated beyond some limit like 80 characters. i.e. avoid print formats wider than 80 characters.

• If you want to print out part of an array:
              WRITE(7,3)(A(I),I=1,10)
  3           FORMAT(1H0,5E12.2)
  This prints out the first 10 elements of array A in scientific notation, the first 5 on the first line; the next 5 on the next line.

  for printing out every other element of the first 9 elements of array A, try

              WRITE(7,4)(A(I),I=1,10,2)
  4           FORMAT(1H0,5E12.2)

  A(1) A(3) A(5) A(7) and A(9) are printed on one line

  
  Notice the 5 in front of the E in the FORMAT statement. This indicates the number of E formatted numbers to put in a row.

• Another type of repetition of printed items is
              WRITE(7,6)
              WRITE(7,8)(I,A(I),I=1,10)
  6           FORMAT(1H0,2X,'I',5X,'A VALUES',//)
  8           FORMAT(1H0,I4,E12.2)
  
  This creates a label, then a group of two columns. The group is 10 lines long. The label puts text above each column. The slashes are line spaces (line skips). There are several other ways to add text, this example is probably the simplest. For example, information can be encoded into a character string (useful when plotting). Character strings can be read using "A" format.

  You can loop several arrayes at a time

              WRITE(7,5)(I,A(I),B(I),I=1,10)
  5           FORMAT(1H0,I4,2E12.2)
  
  This creates 3 columns.

• Encoding character strings
  This is needed to insert a variable into a character string for plotting.
  Here is an illustrative example. Note that the variable used must be declared as a specific sized character string.
              CHARACTER*8 CHRS
              CHARACTER*10 CHR
              WRITE(CHRS,'(8hPSI SB P)')
              WRITE(CHR,'(4ht = ,f6.2)') t
              CALL PLCHHQ(.5,0.05,CHRS,12.,0.,0.)
              CALL PLCHHQ(.5,0.1,CHR,12.,0.,0.)
  
  The first WRITE call encodes a character string of unchanging text.
  The second WRITE call encodes a character string including a variable t. Note the use of formatting; you can use F, I, A, etc.

  Note that to use the NCAR graphics routine PLCHHQ, one needs to start GKS, have SET ranges defined, etc. If you are unfamiliar, consult our NCAR graphics documentation. Example usage can be found in the atmospheric science group software library.

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